Refer to FIG. 1. When a conventional LED illumination module A20 is arranged inside a casing A10 with an accommodation space, the casing 10 usually has several slots A11 formed on the place where the LED illumination module A20 is installed. However, such a technology has the following disadvantages:    1. The slots A11 are usually insufficient to dissipate the heat generated by the LED illumination module A20; and    2. As the LED illumination module A20 is arranged inside the casing A10, the temperature of the casing A10 will rise when heat cannot be fully dissipated, or even worse: the casing A10 or other elements are damaged.